1. Field of the Invention
The invention relates to an optical recording medium and its recording apparatus and reproducing apparatus. More particularly, the invention relates to an optical recording medium which can record and reproduce information at a high density and a high transfer rate and also relates to its recording apparatus and reproducing apparatus.
2. Description of the Related Background Art
FIGS. 1 and 2 Show optical recording media according to conventional recording systems.
FIG. 1 shows an optical disc of the spiral recording system. In a recording area A of an optical disc 100, an information signal is recorded along a spiral track 103 from a signal track start point S to a signal track end point E.
FIG. 2 shows an optical disc of the double spiral recording system. In the recording area A of an optical disc 101, information signals are recorded along spiral tracks 104 and 105 from a first signal track start point S.sub.1 and a second signal track start point S.sub.2 to a first signal track end point E.sub.1 and a second signal track end point E.sub.2, respectively. Two light beams are simultaneously used when the information signals are recorded to the optical disc of the double spiral recording system or the information signals are reproduced from the optical disc.
In the optical disc of the spiral recording system shown in FIG. 1 and the optical disc of the double spiral recording system shown in FIG. 2, a CAV (Constant Angular Velocity) recording system is adopted. As a light spot approaches the outside in the radial direction of the disc, therefore, a unit recording mark length increases, so that even in case of the information of the same length, the recording mark length needs to be increased on the outer rim side and a recording density cannot be improved.
An optical disc 102 using a 2-zone spiral recording system as shown in FIG. 3, therefore, has been proposed in order to improve the recording density. Each track of an inside recording area A.sub.I and an outside recording area A.sub.0 is concentrically arranged on the optical disc 102. An information signal is recorded in the inside recording area A.sub.I along a spiral track 106 from an inside signal track start point S.sub.I to an inside signal track end point E.sub.I. Similarly, an information signal is recorded in the outside recording area A.sub.0 along a spiral track 107 from an outside signal track start point S.sub.0 to an outside signal track end point E.sub.0. Even in the optical disc using the 2-zone spiral recording system, two light beams are simultaneously used when the information signals are recorded and reproduced.
In the optical disc shown in FIG. 3, although a data transfer rate of the inside recording area A.sub.I differs from a data transfer rate of the outside recording area A.sub.0, the sum of the data transfer rates of both areas is always constant.
In the optical disc using the 2-zone spiral recording system, the recording density of the outside recording area A.sub.0 can be raised to a value larger than that of the inside recording area A.sub.I (namely, the data transfer rate can be, raised) and the recording density of the whole optical disc 102 can be increased.
In the image processes of a high definition television such as a high vision television, however, an amount of information to be processed per unit time is fairly large. There is, consequently, a problem such that the recording density is further raised than that of the optical disc shown in FIG. 3 and, at the same time, a high data transfer rate has to be realized.